AN ELECTROPHYSIOLOGICAL SURVEY OF FROG OLFACTORY CILIA

Individual olfactory receptor neurons vary widely in their responses t o odorants. Olfactory stimulus reception occurs in the cilia of the re ceptor neurons. Thus, the variability among individual neurons could i n part be due to differences among the olfactory cilia. We have quanti fied the known conductance properties of each of 117 frog olfactory ci lia. From a strictly qualitative viewpoint, the cilia were very homoge neous. All but a few of them had a basal conductance in the absence of odorants and second messengers, conductances stimulated by cytoplasmi c cyclic AMP and by Ca2+ and a conductance measured in the presence of ATP and stimulated by GTP gamma S. However, the magnitudes of the con ductances varied widely among the cilia. Amplitudes of the cyclic-AMP- and Ca2+-activated ciliary currents correlated strongly with one anot her across the 117 cilia and 24 frogs studied, suggesting that express ion of the underlying channels may be co-regulated. None of the conduc tance properties correlated strongly with ciliary length, a marker of cell maturity. Given cytoplasmic MgATP as substrate, ciliary adenylate cyclase apparently produced cyclic AMP, which in turn gated membrane channels and increased the ciliary conductance. In some cilia, MgATP a lone caused a very large increase in conductance. In others, there was little effect unless GTP gamma S, which increases cyclase activity, w as also added. No effect of cytoplasmic inositol trisphosphate on cili ary conductance was detectable.